Telegraph system



ug 8, 1933- B. P. HAMlLToN 1,921,079

TELEGRAPH SYSTEM Filed Nov. 26. 1932 BY W ATTORNEY Patented Aug. 8, 1933 TELEGRAPH SYSTEM v Baxter I. Hamilton, River Edge, N. J., assignor to American Telephone and Telegraph Com-v pany, a Corporation of New York Application November 26, 1932 Serial No. 644,523

3 Claims.

In telegraph systems the circuits are usually arranged so that an operator may interrupt or break another operator sending signals from some distant point in the telegraph circuit in order to obtain control o f the circuit. The usual method of breaking the circuit is for the operator to open his key for a short interval of time. It is essential that the circuits be arranged so that the first opening of the operators key will cause a clean cut spacing signal to be transmitted to the sending operator, thereby interrupting his sending of signals. When this occurs the sending operators loop will be in the spacing condition even when his key is closed.

It is in general the object of this invention to provide improved arrangements for this apparatus by providing at a telegraph station arrangements whereby the armature of the receiving relay is maintained on its marking contact Whenever the armature of the sending relay is on its spacing contact, thus rendering the incoming signals to the receivingrelay ineffectual to the loop circuit and allowing a spacing signal to be transmitted to the sending operator, the spacing signal causing like battery polarities to be connected to both ends of the loop circuit and interrupting the sending.

The breaking feature of a 'telegraph system is generally accomplished by a break relay which forms equipment furnished in addition to the sending and receiving relays of the telegraph repeater. Another object of this invention is to eliminate this additional equipmentthat is, the break relay, and to accomplish the purpose of such a relay by means of the sending relay, receivingrelay and associated circuits.

While this invention will be pointed out with particularity in the appended claims, the invention itself, both as to its further objects and features, will be better understood from the detailed description hereinafter following, when read in connection with the accompanying drawing which shows one embodiment of the invention given merely for the purpose of illustration.

Referring to the drawing, there is shown one terminal ci a carrier telegraph channel at which there is a line L1 over which signals coming in from a distant station may be received and a line L2 over which signals may be transmitted to a distant station. The received currents from line L1 flow through a receiving lter F1, an ampliier A, and to a vacuum tube V by means of transformer T. It will be apparent that pulses ofv alternating current corresponding to telegraph signals will appear in the input circuit of the tube V. i

The output circuitV ofthe tube V includes the y battery B1, the main line winding W3 of the polarreceiving relay R1, theprimary Winding W1 of a kick transformer T1, the plate and filament electrodes of the tube V and ground. The tube V is employed to act as a rectier, and by virtue of its rectifying properties the current iiowing in its output circuit will be a direct current, interrupted in accordance with the telegraph signals. Each pulse of alternating current in the input circuit of the tube V will produce. a corresponding direct current pulse in the output circuit of the tube V.

The receiving relay R1 includes, in addition to the main winding vW3, a kick winding W4, and a biasing winding W5. The winding W5 is connected in a series circuit which includes a battery E2, a resistance Z1, the winding W5 itself, and ground. Current flows continuously through the latter circuit and the effect produced by winding W5 tends to move the armature oi the relay R1 toward its spacing contact S, and if this armature is already on the spacing Contact S the magnetic effect of Winding W5 will tend to hold it on this contact. The magnitude of the biasing effect of winding W5 is generally about one-half the magnetic effect which may be produced by the winding W3 and, moreover, the effects of windings W3 and W5 which are mutually opposite.

The kick Winding W4 ofthe receiving relay R1 is connected to the secondary W2 of transformer T1, the only purpose being to aid or accelerate the movement of the armature between contacts M and S. As an incoming pulse of carrier causes a current to build up in the output circuit of tube V, a secondary pulse of current iiows through windings W2 and W4 in a direction which aids the movement of the armature of the receiving relay R1 fromV contact S to contact M. Similarly, when the incoming pulse of carrier is dying away, a secondary pulse is introduced in the opposite direction in the circuit of windings W2 and W4 and aids the movement of the armature of relay'R1 from contact M to contact S.

The armature oi receivingV relay R1 is connected -to the midpoint of a balanced loop'circuit, one branch containing winding We of the sending relay R2, a variable resistance Z2, and a loop circuit which includesv a telegraph'key a sounder N1, and a battery B3 as well as ground, the other branch containing winding W1 of the sending relay R2 and Va fixed resistance Z3 as well as ground. The `resistance Z3 is simply used for balancing purposes. The key E and the sounder N1 may be considered the equipment at a local station and this circuit is generally known as a loop.` The resistance Z2 is generally adjusted so that the resistance ofV designated M and S, and these are generally known as marking and spacing contacts, respectively. These contacts are connected to oppositely poled batteries B4 and B5, both of which are grounded. When the armature of the relay.

R1 is in its mid-position and free 'from its contacts M and S and key E is open, no current will flow through the windings We or W7 of the sending relay R2. When the contact M of the relay R1 becomes closed and key E at the loop is also closed, current will then flow through the winding We of the relay R2 and its magnitude will be about twice as great as that flowing through the winding W7, Since the magnetic eiiects of windings `We and W7 are arranged to be mutually opposite, and since the magnetic effect of winding WG is greater, it will tend to move the armature of the relay R2 towards its marking contact M or to hold it on contact M if it is already there. When the armature of the relay R1 closes its spacing contact S, the magnetic effect of the winding W7 will be reversed, tending to maintain the armature of the relay R2 closed against its marking contact M. While this condition exists the battery B4, which is connected to the spacing contact S of the` relay R1, will oppose the battery B3, If key E is closed, since the voltages of these batteries, i. e, batteries B3 and Bi are practically equal to each other, no current will flow through the winding We. It the key E is open, no current will new through the winding W1; of the relay R2 as was the case when the key E was closed.

It will be seen that as long as the key E is open there will be no magnetic effect whatever .in the winding Ws of the sending relay R2.

Under this condition the magnetic effect of the winding W7 of the reiay R2 would be dependent upon the position of the armature of the relay R1. If the armature of the relay R1 is on its marking contact M, the armature of the relay R2 will go to its spacing contact. However, if the armature of the relay R1 is on its spacing contact the armature of the relay R2 will go to its marking contact. Thus, when the winding WG of the relay R2 becomes effectively deenergized, the armature of the relay R2 will close its spacing contact S when the armature of the relay R1 closes its marking contact, and conversely the'armature of the relay R2 will close its marking Contact M when the armature of the relay R1 closes its spacing contact S.

Under these conditions if a break feature, which will be described hereinafter, were not incorporated in-the system, signals received over the circuit L1 would be retransmitted over the circuit L2 in reversed form, and this would occur ior a period of time which depends upon the length and characteristic of the line circuit.

The armature of the relay R2 and its spacing contact S lead to an alternating current generator G which is connected in series with a resistance Z4. The generator G and its resistance Z4 are also connected to a sending iilter F2, which extends to the output circuit L2, and the circuit L2 leads to a distant station. Just as the circuit L1 receives alternating current signaling pulses from a distant station so the circuit L2 sends alternating current signaling pulses to a distant station,.which may be, and preferably is,

the same station connected or coupled to the circuit L1. Thus, it will be seen that the circuits L1 and L2 form a four-wire arrangement suitable for the transmission of pulses of alternating current in opposite directions between a pair of stations.

It is to be noted that when the spacing contact S of the relay is closed by its armature, the generator G will be short-circuited through the resistance Zi, and practically no current will ow from theV generator G through the ilter F2 over the circuit L2. When the contact S of the relay R2 is open, alternating current will be transmitted from the generator G through lter F2 and over the circuit L2. Thus, signals composed of pulses or aiternating current may be transmitted over the circuit L2 in accordance with the operation ofthe armature of therelay R2.

`The armature of the relay R2 groundedf The contact M of the relay R2 is connected to a circuit containing resistance Z5, a telegraph sounder N2 shunted by resistance Z5, a positive battery BG, and ground. The contact M is also connected to a circuit containing resistance Z7, 1n

which is also in turn connected to the grid circuit o the tube V and to resistance Z8 and negative battery B7. Normally the grid circuit of the tube "-J is held at a negative potential of about 40 volts to allow the tube to operate as a rectifier. This potential is applied to the grid of the tube V through the winding of transformer T1, the resistance Z8, and negative battery B1. When the armature or the sending relay R2 is on its marking contact M, a ground is connected to the circuit between resistances Z5 and Z7. This will cause a small current to flow in the circuit from the battery B7 through resistances Za and Z7, and to ground at Contact M and the armature of relay R2. ZS of the order ci megohms are so proportioned that this small current will cause a voltage drop in resistance Z8 which when addedV algebraically to the voltageof battery B7 will provide the 'correct negative grid bias for the tube V to operate as a rectifier, 'that is, approximately 40 volts. t is thus apparent that under this condition the tube V can operate in a normal way as a rectifier, and each pulse oi alternating current j in the input circuit will produce a corresponding pulse of direct current in the output circuit. The ground between resistances Z5 and Z7 will also'cause a current to flow from battery BG through the sounder N2 and shunt Ze, through Z5 and to ground through the contact M and armature of relay The current through the sounder N2 will be sufficient to operate this sounder.

When the armature of the sending relay R2 is not on its marking contact M, the ground on the circuit between Z5 and ZG will be removed. This will allow positive battery EG to exert its influence in reduoingthe negative potential applied to the grid oi' tube V to practically zero.

This will cause an output current in the plate circuit o1 the tube V regardless oi' whether or not there incoming carrier current in the line circuit L1. This output current will be eiective The resistances Z7 and f in moving the armature of relay R1 towards its marking contact M if the armature is not already on this Contact.. It is thus apparent that under this condition the tube V is not in a condition to receive signals from the distant station but will keep the armature of relay R1 against its marking Contact M as long as the armature of the sending relay R2 is not on its M contact. The resulting currentwhich will iiow from battery Ba through the sounder N2, resistance Z5, resistance Z7, resistance Z8 and battery B7 to ground is Very small in magnitude, generally of the order of a fraction of a milliampere, and the sounder N2 will be released. The sounder N2 will be closed when the armature of relay Rz is on its Contact M and Will release when the armature of relay R2 is not on its contact M and will thus enable outgoing signals to be read. Y

'I'he operator at the loop may desire to send signals over the circuit L2 to the distant station. This he may do by opening .his key E in order to gain control of the circuit and break the transmission of signals from the distant station over the circuit L1. If the armature of the relay R1 is on its spacing contact S, the armature of the relay R2 will remain on its marking contact M and generator G will continue to send current through iilter F2 over the circuit L2. Still there will be no break in the circuit. When, under the control of incoming signals, the armature of the relay R1 goes to its marking Contact M, the armature of the relay R2 will reach its spacing contact S, and generator G will be short-circuited through the resistance Zi. No current will then be 'transmitted by the generator G over the circuit L2. If no break feature were provided and a spacing signal were to be received before the breaking signal had reached the operator at the distant station, the armature of the relay R1 would be operated to its spacing contact S, thereby causing the armature of sending relay R2 to move to its marking contact. This would interrupt the breaking signal.

A special feature of this invention lies in the prevention of the armature of the relay R1 from leaving its marking contact M after it has reached this contact and after the key E has been opened by the operator at the loop for the purpose of breaking the circuit. Since armature of the sending relay R2 will thereby be operated to its spacing contact S, the ground Will be removed from the circuit between resistances Z5 and Z7. This Will reduce the negative potential on the grid of the tube V and cause a steady plate current to iiow from battery B1 through the Winding W3 of the relay R1, Winding W1 of transformer T and the plate and filament electrodes of the tube V and ground, and the current through Winding Wa Will be sufficient to cause the armature of relay R1 to close to its marking contact M. If, as here shown, the marking contact of relay R1 is maintained closed, the spacing contact of the relay R2 Will also remain closed and no current Will iiow from the generator over the circuit L2. It is essential to maintain the spacing Contact of the relay R2 closed for a suicient interval of time so that the spacing or breaking signal to the distant station located at the distant end of the circuit L2 will be completed and registered.

While this invention has been shown and described in certain particular arrangements merely for the purpose of illustration, it Will be understood that the general principles of this invention may be applied to other and Widely varied organizations Without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. In a telegraph system having a line over which signals are transmitted and a line over which signals are received, the combination of a receiving relay, a sending relay, a detector tube which is normally highly biased and is interposed between the receiving line and the receiving relay and acts as a rectifier when so biased, a loop including a key connected to the receiving relay through the sending relay, and means responsive to the breaking of the circuit by the opening of the key at the loop toA bring the armature of the sending relay and the armature of the receiving relay into predetermined positions and to maintain these armatures in said predetermined positions as long as the key remains open, said means including means to substantially reduce the bias of the detector tube so that it can not act as a rectier.

2. In a telegraph system having a line over Which signals are transmitted and a line over which signals are received, vthe combination of a receiving relay, a sending relay, a detector tube which is normally highly biased and is interposed between the receiving line and the receiving relay and acts as a rectier when so biased, a loop including a key connected to the receiving relay through the sending relay, means responsive to the breaking of the circuit by the opening of the key at the loop to bring the armature of the sending relay and the armature of the receiving relay into predetermined positions and to maintain these armatures in said predetermined positions as long as the key remains open, said means including means to substantially reduce the bias of the `detector tube so that it can not act as a rectier, and a sounder which is controlled by the armature of the sending relay. l

3. In a telegraph system having a line over which signals are transmitted and a line over Whichsignals are received, the combination of means including a vacuum tube having plate, filament and grid electrodes, the grid and lament electrodes of said vacuum tube being impressed With pulsesof alternating current corresponding to telegraph signals received over the receiving line, the grid electrode of the vaelay also controlling the transmission of alternatv ing current over the sending line, and means controlled by the sending relay and responsive to the opening of the key included in the loop to substantially reduce the negative bias o-n the grid electrode of the vacuum tube with respect to the filament electrode and bring the armature of the receiving relay to a predetermined posi-- tion and maintain it in that position while the key of the loop remains open.

BAXTER P. HAMILTON. 

